MEMS device and fabrication method of the same

ABSTRACT

A microelectromechanical systems (MEMS) device includes a frame, an actuator formed on the same layer as the frame and connected to the frame to be capable of performing a relative motion with respect to the frame, and at least one stopper restricting a displacement of the actuator in a direction along the height of the actuator. The MEMS device is fabricated by bonding a second substrate to a first substrate, forming the frame and the actuator by partially removing the first substrate, and forming the at least one stopper by partially removing the second substrate.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This is a Divisional of application Ser. No. 11/873,008 filed on Oct.16, 2007 which claims priority from Korean Patent Application No.10-2007-0007915, filed on Jan. 25, 2007, in the Korean IntellectualProperty Office. The entire disclosures of the prior applications areconsidered part of the disclosure of the accompanying divisionalapplication and are hereby incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Apparatuses and methods consistent with the present invention relate toa microelectromechanical systems (MEMS) device, and more particularly,to a MEMS device which can reduce damage due to an external shock bylimiting the displacement of an actuator in a height direction, and amethod of fabricating the MEMS device.

2. Description of the Related Art

Recently, a study on a MEMS device having a fine structure fabricated bymicromachining technology has been actively performed in the technicalfields of displays, laser printers, precision measurement, and precisionprocessing. For example, in the display field, the MEMS device ishighlighted for being used as an optical scanner to deflect and reflectscanning light to a screen.

A related art MEMS device mainly used as an optical scanner includes aframe and an actuator connected to the frame by a predetermined pivotaxis to be capable of pivoting. The actuator is formed on the same layerwith the frame and inside the frame. When an external shock in adirection along the plane is applied to the MEMS device, since the frameformed on the same layer with the actuator limits the excessivedisplacement of the actuator in the plane direction, damage to the MEMSdevice in spite of a relatively large external shock can be reduced.However, when an external shock is applied to the MEMS device in aheight direction, since there is no part to limit the displacement ofthe actuator in the height direction, the MEMS device can be easilydamaged permanently by a small external shock.

SUMMARY OF THE INVENTION

To address the above and/or other aspects, the present inventionprovides a microelectromechanical systems (MEMS) device which can reducedamage due to an external shock by limiting the displacement of anactuator in the height direction, and a method of fabricating the MEMSdevice.

According to an aspect of the present invention, a MEMS device comprisesa frame, an actuator formed on a same layer as the frame and connectedto the frame to be capable of performing a relative motion with respectto the frame; and at least one stopper which restricts a displacement ofthe actuator in a direction along a height of the actuator.

The stopper may comprise an ascending restriction stopper restricting anupward displacement of the actuator and a descending restriction stopperrestricting a downward displacement of the actuator.

The ascending restriction stopper may be fixed to the frame and includean end portion that overlaps the actuator by being separated apredetermined distance from the actuator when there is no displacementof the actuator.

The descending restriction stopper may be fixed to the actuator andinclude an end portion that overlaps the frame by being separated apredetermined distance from the frame when there is no displacement ofthe actuator.

The MEMS device may further comprise a stage fixed to the actuator.

The stopper may be formed on the same layer as the stage.

The MEMS device may further comprise a separation column providedbetween the actuator and the stage to restrict deformation of the stagedue to thermal deformation of the actuator.

A circular opening portion to restrict thermal transfer between thestage and the actuator may be formed in a peripheral area of an areawhere the actuator is coupled to the separation column.

The MEMS device may further comprise a light reflection surface formedon an upper surface of the stage.

The actuator may be connected to the frame to be capable of pivotingwith respect to the frame.

The MEMS device may further comprise an electrostatic capacity sensordetecting an amount of pivot of the actuator.

The electrostatic capacity sensor may comprise a drive comb pivotingwith the actuator according to the pivot of the actuator, and a fixedcomb fixedly supported at a complementary position where the fixed combis engaged with the drive comb and forming an overlapping surface whosearea change according to the pivot of the drive comb.

The actuator may comprise an external variable portion connected to theframe to be capable of pivoting about a first pivot axis with respect tothe frame, and an internal variable portion located inside the externalvariable portion to be capable of pivoting about a second axis withrespect to the external variable portion based on a second pivot axisthat is perpendicular to the first pivot axis, and the stopper mayrestrict a displacement of the external variable portion in thedirection along the height of the actuator.

The MEMS device may further comprise a light reflection surface formedon an upper surface of the internal variable portion.

The MEMS device may further comprise a drive coil wound around aperipheral portion of the actuator, and at least one magnet forming amagnetic field that crosses current flowing in the drive coil.

According to another aspect of the present invention, a method offabricating a MEMS device comprises bonding a second substrate to afirst substrate, forming a frame and an actuator connected to the frameto be capable of performing a relative motion with respect to the frameby partially removing the first substrate, and forming at least onestopper restricting a displacement of the actuator in a direction alongthe height of the actuator by partially removing the second substrate.

The first and second substrates may be formed of silicon (Si).

The forming of an actuator may comprise forming the actuator connectedto the frame to be capable of pivoting with respect to the frame.

The forming of at least one stopper may comprise forming an ascendingrestriction stopper restricting an upward displacement of the actuatorand a descending restriction stopper restricting a downward displacementof the actuator.

The method may further comprise partially etching a lower surface of thesecond substrate before bonding the first substrate and the secondsubstrate to allow an end portion of the at least one stopper to beseparated from the first substrate.

The method may further comprise forming a stage fixed to the actuator bypartially removing the second substrate.

The method may further comprise forming a light reflection surface on anupper surface of the stage.

The method may further comprise partially etching a lower surface of thesecond substrate before bonding the first and second substrates to forma separation column provided between the actuator and the stage.

The method may further comprise partially etching an upper surface ofthe first substrate before bonding the first and second substrates toallow an end portion of the stopper to be separated from the firstsubstrate.

The forming of the actuator may comprise forming an external variableportion connected to the frame to be capable of pivoting about a firstpivot axis with respect to the frame, and forming an internal variableportion located inside the external variable portion to be capable ofpivoting about a second pivot axis with respect to the external variableportion, the second pivot axis being perpendicular to the first pivotaxis.

The method may further comprise forming a light reflection surface on anupper surface of the internal variable portion.

The method may further comprise forming a drive coil wound around aperipheral portion of the actuator, and arranging a magnet to form amagnetic field that crosses current flowing in the drive coil.

The forming of the drive coil may comprise forming at least one drivecoil groove by etching a lower surface of the first substrate, anddepositing metal in the at least one drive coil groove.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects of the present invention will become moreapparent by describing in detail exemplary embodiments thereof withreference to the attached drawings in which:

FIGS. 1 and 2 are exploded perspective views of a MEMS device accordingto an exemplary embodiment of the present invention, respectively viewedfrom the top and bottom sides;

FIG. 3 is a partially cut-away view of the MEMS device taken along lineA-A′ of FIG. 1, according to an exemplary embodiment of the presentinvention;

FIGS. 4A and 4B are sectional views taken along line A-A′ of FIG. 1, inwhich FIG. 4A illustrates that the actuator ascends by an external shockand FIG. 4B illustrates that the actuator descends by an external shock,according to an exemplary embodiment of the present invention;

FIGS. 5A and 5F are sectional views sequentially illustrating theprocess of fabricating the MEMS device of FIG. 1, according to anexemplary embodiment of the present invention;

FIGS. 6 and 7 are exploded perspective views of a MEMS device accordingto another exemplary embodiment of the present invention, respectivelyviewed from the top and bottom sides;

FIG. 8 is a partially cut-away view of the MEMS device of FIG. 6,according to an exemplary embodiment of the present invention;

FIG. 9 is a perspective view of a MEMS device according to yet anotherexemplary embodiment of the present invention;

FIGS. 10 and 11 are enlarged perspective views of a portion B of FIG. 9,respectively viewed from the top and bottom sides, according to anexemplary embodiment of the present invention;

FIGS. 12 and 13 are perspective views of a MEMS device according to yetfurther another embodiment of the present invention, respectively viewedfrom the top and bottom sides, according to an exemplary embodiment ofthe present invention;

FIG. 14 is an enlarged plan view of a portion C of FIG. 12, according toan exemplary embodiment of the present invention; and

FIG. 15 is a partially cut-away perspective view taken along line D-D′pf FIG. 14, according to an exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIGS. 1 and 2 are exploded perspective views of a microelectromechanicalsystems (MEMS) device according to an exemplary embodiment of thepresent invention, respectively viewed from the top and bottom sides.FIG. 3 is a partially cut-away view of the MEMS device taken along lineA-A′ of FIG. 1. FIGS. 4A and 4B are sectional views taken along lineA-A′ of FIG. 1, in which FIG. 4A illustrates that the actuator ascendsby an external shock and FIG. 4B illustrates that the actuator descendsby an external shock.

Referring to FIGS. 1 through 3, a MEMS device 100 according to anexemplary embodiment of the present invention includes a frame 111 fixedto a predetermined support, an actuator 115 connected to the frame 111to be capable of pivoting about a pivot axis S with respect to the frame111, and a stage 132 fixed to the actuator 115. The actuator 115 isarranged at the center portion of the frame 111 and connected to theframe 111 by a pair of torsion springs 113. The frame 111, the actuator115, and the torsion springs 113 are formed on the same layer becausethey are formed by processing a first substrate 110.

The MEMS device 100 includes a drive coil 120 wound around a peripheralportion of the bottom surface of the actuator 115. The MEMS device 100further includes a pair of magnets 105 and 106 arranged at the oppositesides of the frame 111 to face each other to form a magnetic field thatcrosses current flowing in the drive coil 120. A terminal 125 isconnected to external power to apply current to the drive coil 120. Theactuator 115 pivots in a direction according to the Lorentz's Law by theinteraction between the current flowing the drive coil 120 and amagnetic field formed in a direction crossing a pattern of the drivecoil 120 by the magnets 105 and 106. When the current is discontinued,the actuator 115 returns to a state of being parallel to the frame 111by an elastic restoration force of the torsion springs 113.

A light reflection surface 135 formed by depositing light reflectionsubstances is provided on the upper surface of the stage 132. When thecurrent flows in the drive coil 120, the drive coil 120 thermallyexpands by its own resistance so that the actuator 115 can be deformed.To restrict the deformation of the stage 132 due to the deformation ofthe actuator 115, a separation column 133 is provided between the stage132 and the actuator 115. The stage 132 and the actuator 115 areseparated as much as the height d1 of the separation column 133. Tominimize the effect on the stage 132 by the thermal deformation of theactuator 115, the bottom surface of the separation column 133 adheringto the actuator 115 is set to be smaller than the light reflectionsurface 135 of the stage 132.

The MEMS device 100 includes a stopper restricting the displacement ofthe actuator 115 in the height direction. The stopper includes anascending restriction stopper 140 restricting the upward displacement ofthe actuator 115 and a descending restriction stopper 150 restrictingthe downward displacement of the actuator 115. The stoppers 140 and 150and the stage 132 are formed on the same layer because they are formedby processing a second substrate 130 adhering to the first substrate110.

The ascending restriction stopper 140 extends from a fixing portion 139adhering to the frame 111 and is fixed with respect to the frame 111.The ascending restriction stopper 140 includes an end portion 141 thatoverlaps the peripheral portion of the actuator 115 by being separated apredetermined distance d2 therefrom when there is no displacement of theactuator 115 in the height direction. The descending restriction stopper150 is fixed with respect to the actuator 115 as an adhering surface 152of the descending restriction stopper 150 adheres to the upper surfaceof the actuator 115. The descending restriction stopper 150 includes anend portion 151 that overlaps the frame 111 by being separated apredetermined distance d3 therefrom when there is no displacement of theactuator 115 in the height direction. The height d1 of the separationcolumn 133, the separation distance d2 of the ascending restrictionstopper 140, and the separation distance d3 of the descendingrestriction stopper 150 are formed by etching the lower surface of thesecond substrate 130 so that the d1, d2, and d3 can be identical to oneanother.

Referring to FIG. 4A, when an external shock is applied to the MEMSdevice 100 so that the actuator 115 ascends suddenly, since theperipheral portion of the actuator 115 is caught by the end portion 141of the ascending restriction stopper 140, the excessive ascending of theactuator 115 is prevented. Referring to FIG. 4B, when an external shockis applied to the MEMS device 100 so that the actuator 115 descendssuddenly, since the end portion 151 of the descending restrictionstopper 150 descending with the actuator 115 is caught by the frame 111,the excessive descending of the actuator 115 is prevented. Accordingly,the damage of the MEMS device 100, in particular, the damage of thetorsion springs 113, due to the external shock, is prevented.

FIGS. 5A and 5F are sectional views sequentially illustrating theprocess of fabricating the MEMS device of FIG. 1. Referring to FIG. 5A,the first and second substrates 110 and 130 are prepared. The first andsecond substrates 110 and 130 may be formed of silicon (Si) exhibitingsuperior processing and evenness characteristics. The upper surface ofthe first substrate 110 is oxidized to form an insulation layer 117. Thelower surface of the second substrate 130 is partially etched to formgrooves 160 to form the distance d1 of the stage 132 of FIG. 3, thedistance d2 of the ascending restriction stopper 140 of FIG. 3, and thedistance d3 of the descending restriction stopper 150 of FIG. 3. Themethod of forming the grooves 160 includes sand blasting or dry or wetetching after forming a pattern by photolithography, which is well knownin the semiconductor fabrication process.

Referring to FIG. 5B, the second substrate 130 is bonded to the firstsubstrate 110. When the first and second substrates 110 and 130 areformed of silicon (Si), the first and second substrates 110 and 130 canbe bonded in a silicon direct bonding (SDB) method. Next, the thicknessof the first substrate 110 is grinded corresponding to the thickness ofthe actuator 115 of FIG. 3 and the frame 111 of FIG. 3, and a drive coilgroove 118 is formed by etching the lower surface of the first substrate110. The method of fabricating the drive coil groove 118 includes sandblasting or dry or wet etching after forming a pattern byphotolithography, which is well known in the semiconductor fabricationprocess. Next, an insulation layer 119 is formed on the drive coilgroove 118.

Referring to FIG. 5C, a drive coil 120 is formed by depositing metal,for example, copper (Cu) in the drive coil groove 118. The drive coil120 can be formed by depositing metal or plating metal after depositinga metal seed layer (not shown) in the drive coil groove 118.

Referring to FIG. 5D, an insulation layer 122 is formed on the lowersurface of the first substrate 110 where the drive coil 120 is formedand the terminal 125 for connecting the drive coil 120 to the externalpower is formed. The second substrate 130 is grinded corresponding tothe thicknesses of the stage 132 of FIG. 3, the stoppers 140 and 150 ofFIG. 3, and the fixing portion 139 of FIG. 3.

Referring to FIG. 5E, the first substrate 110 is partially removed so asto be penetrated in a direction of the thickness of the first substrate110 to form the frame 111, the actuator 115, and the torsion springs113. Referring to FIG. 5F, the second substrate 130 is partially removedso as to be penetrated in a direction of the thickness of the secondsubstrate 130 to from the stage 132, the ascending restriction stopper140, the descending restriction stopper 150, and the fixing portion 139.

Next, a metal light reflective substance is deposited on the uppersurface of the stage 132 to form the light reflection surface 135. Themagnets 105 and 106 of FIG. 1 are arranged to face each other withrespect to the frame 111. The MEMS device 100 fabricated as above isused as an optical scanner.

FIGS. 6 and 7 are exploded perspective views of a MEMS device accordingto another exemplary embodiment of the present invention, respectivelyviewed from the top and bottom sides. FIG. 8 is a partially cut-awayview of the MEMS device of FIG. 6. FIG. 9 is a perspective view of aMEMS device according to yet another exemplary embodiment of the presentinvention. FIGS. 10 and 11 are enlarged perspective views of a portion Bof FIG. 9, respectively viewed from the top and bottom sides.

Referring to FIGS. 6 through 8, a MEMS device 200A according to anotherexemplary embodiment of the present invention includes a frame 211 fixedto a base 201, an actuator 215 connected to the frame 211 to be capableof pivoting about a pivot axis S with respect to the frame 211, and astage 232 fixed to the actuator 215. The actuator 215 is arranged at thecenter portion of the frame 211 and connected to the frame 211 via apair of torsion springs 213. The frame 211, the actuator 215, and thetorsion springs 213 are formed on the same layer because they are formedby processing a first substrate 210. The base 201 can be formed ofsilicon (Si) or glass, and an opening 202 is formed at the centerportion of the base 201 not to prevent pivoting of the actuator 215.

A drive coil 220 is wound around a peripheral portion of the bottomsurface of the actuator 215. A pair of magnets 205 and 206 are arrangedat the opposite sides of the frame 211 to face each other. The actuator215 pivots in a direction according to the Lorentz's Law by theinteraction between current flowing the drive coil 220 and a magneticfield formed in a direction crossing a pattern of the drive coil 220 bythe magnets 205 and 206. When the current is discontinued, the actuator215 returns to a state of being parallel to the frame 211 by an elasticrestoration force of the torsion springs 213.

A light reflection surface 235 is provided on the upper surface of thestage 232. A separation column 233 to restrict the deformation of thestage 232 due to the thermal deformation of the actuator 215 is providedbetween the stage 232 and the actuator 215. A circular opening 263 torestrict thermal transfer between the stage 232 and the actuator 215 isformed around an area where the separation column 233 is coupled to theactuator 215.

The MEMS device 200A includes an ascending restriction stopper 240Arestricting the upward displacement of the actuator 215 and a descendingrestriction stopper 250A restricting the downward displacement of theactuator 215. The stoppers 240A and 250A and the stage 232 are formed onthe same layer because they are formed by processing a second substrate230 adhering to the first substrate 210.

The ascending restriction stopper 240A extends from a fixing portion 239adhering to the frame 211, and is fixed with respect to the frame 211.The ascending restriction stopper 240A is separated a predetermineddistance from the frame 211 and extends toward the peripheral portion ofthe actuator 215. The ascending restriction stopper 240A includes an endportion 241A that overlaps the peripheral portion of the actuator 215 bybeing separated a predetermined distance therefrom when there is nodisplacement of the actuator 215 in the height direction.

The descending restriction stopper 250A is fixed with respect to theactuator 215 as an adhering surface 252 of the descending restrictionstopper 250A adheres to the upper surface of the actuator 215. Thedescending restriction stopper 250A includes an end portion 251Abranched with respect to the ascending restriction stopper 240A andextending toward the frame 211. When there is no displacement of theactuator 215 in the height direction, the end portion 251A of thedescending restriction stopper 250A overlaps the frame 211 by beingseparated a predetermined distance therefrom.

When an external shock is applied to the MEMS device 200A so that theactuator 215 ascends suddenly, since the peripheral portion of theactuator 215 is caught by the end portion 241A of the ascendingrestriction stopper 240A, the excessive ascending of the actuator 215 isprevented. Also, when an external shock is applied to the MEMS device200A so that the actuator 215 descends suddenly, since the end portion251A of the descending restriction stopper 250 descending with theactuator 215 is caught by the frame 211, the excessive descending of theactuator 215 is prevented. Accordingly, the damage of the MEMS device200A, in particular, the damage of the torsion springs 213, due to theexternal shock, is prevented.

The MEMS device 200A further includes an electrostatic capacity sensorfor detecting an amount of pivot of the actuator 215. The electrostaticcapacity sensor includes a plurality of drive combs 260 extending fromthe descending restriction stopper 250A in a direction crossing thepivot axis S, and a plurality of fixed combs 261 fixed to the frame 211.The drive combs 260 pivot together with the actuator 215 and the stage232 at the same angle as a pivot angle of the actuator 215 and the stage232. The fixed combs 261 are fixedly supported at complementarypositions so as to be engaged with the drive combs 260.

The fixed combs 261 and the drive combs 260 form an overlapping surfacewhere they overlap each other. The area of the overlapping surfacechanges according to the pivot amount of the actuator 215. When apredetermined electric potential difference is given between the drivecombs 260 and the fixed combs 261 where the overlapping surface isformed, an electrostatic capacity having a functional relationship withthe pivot amount of the actuator 215 is formed. Thus, the pivot amountof the actuator 215 and the stage 232 can be measured by measuring theelectrostatic capacity between the drive combs 260 and the fixed combs261.

Referring to FIGS. 9 through 11, a MEMS device 200B according to yetanother exemplary embodiment of the present invention, which is amodified example of the above-described MEMS device 200A, has the samestructure as that of the MEMS device 200A except for the structures ofan ascending restriction stopper 240B and a descending restrictionstopper 250B. The descending restriction stopper 250B of the MEMS device200B according to the present exemplary embodiment includes an endportion 251B branched not to cover the torsion springs 213 and extendingtoward the frame 211. The end portion 251B of the descending restrictionstopper 250B includes a groove 252 cut upwardly and separated from apredetermined distance from an end portion 212 of the frame 211 whenthere is no displacement of the actuator 215 in the height direction,and a connection portion 253 provided at an end portion of the groove252. An actuator piece 216 is bonded to the connection portion 253.Since the actuator piece 216 is separated from the frame 211, theactuator piece 216 moves according to the ascending/descending orpivoting of the actuator 215. The ascending restriction stopper 240Bprotrudes from the fixed portion 239 to face the connection portion 253of the descending restriction stopper 250B. The ascending restrictionstopper 240B is separated a predetermined distance from the actuatorpiece 216 when there is no displacement of the actuator 215 in theheight direction.

When an external shock is applied to the MEMS device 200B so that theactuator 215 ascends suddenly, since the actuator piece 216 boned to theconnection portion 253 is caught by the ascending restriction stopper240B, the excessive ascending of the actuator 215 is prevented. Also,when an external shock is applied to the MEMS device 200B so that theactuator 215 descends suddenly, since the groove 252 of the descendingrestriction stopper 250B descending with the actuator 215 is caught bythe end portion 212 of the frame 211 fixedly connected to the frame 211,the excessive descending of the actuator 215 is prevented. Accordingly,the damage of the MEMS device 200B, in particular, the damage of thetorsion springs 213, due to the external shock, is prevented.

FIGS. 12 and 13 are perspective views of a MEMS device according to yetfurther another exemplary embodiment of the present invention,respectively viewed from the top and bottom sides. FIG. 14 is anenlarged plan view of a portion C of FIG. 12. FIG. 15 is a partiallycut-away perspective view taken along line D-D′ pf FIG. 14.

Referring to FIGS. 12 through 15, a MEMS device 300 according to yetfurther another exemplary embodiment of the present invention includes abase 301 having an opening 302 at the center portion thereof, a firstsubstrate 310 adhering to the base 301 and a second substrate 330adhering to the first substrate 310. The base 301 can be formed ofsilicon (Si) or glass while the first and second substrates 310 and 330can be foamed of silicon.

The first substrate 310 includes an actuator 315 arranged in an opening302 of the base 301 to be capable of pivoting, and a frame (not shown)bonded and fixed to the base 301. The second substrate 330 includes afixed portion 339 bonded and fixed to the frame of the first substrate310 and an ascending restriction stopper 340 and a descendingrestriction stopper 350 restricting the displacement of the actuator 315in the height direction.

The actuator 315 includes an external variable portion 318 connected tothe frame to be capable of pivoting about a first pivot axis S1 withrespect to the frame, an internal variable portion 316 capable ofpivoting with respect to the external variable portion 318 based on asecond pivot axis S2 crossing the first pivot axis S1, and a filtervariable 317 provided between the internal variable portion 316 and theexternal variable portion 318. The external variable portion 318 isconnected to the frame of the first substrate 310 by a pair of firsttorsion springs 322 extending in the same direction as the first pivotaxis S1. The filter variable portion 317 is connected to the externalvariable portion 318 by a pair of filter springs 323 extending in thesame direction as the first torsion springs 322. The internal variableportion 316 is connected to the filter variable portion 317 by a pair ofsecond torsion springs 324 extending in the same direction as the secondpivot axis S2.

A drive coil 320 is formed around a lower surface of the externalvariable portion 318. A pair of magnets 305 and 306 are arranged to faceeach other with respect to the base 301, the first substrate 310, andthe second substrate 330. The direction of magnetic field lines formedby the magnets 305 and 306 is inclined with respect to the first pivotaxis S1 and the second pivot axis S2. When current is applied to thedrive coil 320, torque is generated in a direction perpendicular to thedirection of the current and a magnetic field formed by the magnets 305and 306. The torque is separated into two components of the first pivotaxis S1 and the second pivot axis S2 so that the internal variableportion 316 pivots about the second pivot axis S2. Also, the internalvariable portion 316, the filter variable portion 317, and the externalvariable portion 318 pivot about the first pivot axis S1. A lightreflection surface 335 is formed on the upper surface of the internalvariable portion 316 so that an optical signal incident on the lightreflection surface 335 can be divided into two axes.

The filter variable portion 317 and the filter springs 323 separate theexternal variable portion 318 that pivots at a low frequency, and theinternal variable portion 316 that pivots at a high frequency so thatunnecessary vibrations of the external variable portion 318 due to highfrequency noise is blocked. That is, the filter variable portion 317 andthe filter springs 323 are mechanical configuration of a low passfilter.

The ascending restriction stopper 340 and the descending restrictionstopper 350 are configured to restrict the displacement of the externalvariable portion 318 in the height direction. In detail, the ascendingrestriction stopper 340 is integrally formed with the fixed portion 339of the second substrate 330 to overlap the peripheral portion of theexternal variable portion 318 by being separated a predetermineddistance therefrom when there is no displacement of the externalvariable portion 318 in the height direction. The descending restrictionstopper 350 is bonded to the upper surface of the external variableportion 318 and fixed to the external variable portion 318. Thedescending restriction stopper 350 has an end portion 351 that overlapsa frame peripheral portion 312 outside the external variable portion 318by being separated a predetermined distance therefrom when there is nodisplacement of the external variable portion 318 in the heightdirection.

When an external shock is applied to the MEMS device 300 so that theexternal variable portion 318 ascends suddenly, since the peripheralportion of the external variable portion 318 is caught by the ascendingrestriction stopper 340, the excessive ascending of the externalvariable portion 318 is prevented. Also, when an external shock isapplied to the MEMS device 300 so that the external variable portion 318descends suddenly, since the end portion 351 of the descendingrestriction stopper 350 descending with the external variable portion318 is caught by the frame peripheral portion 312, the excessivedescending of the external variable portion 318 is prevented. Theinternal variable portion 316 hardly ascends or descends with respect tothe external variable portion 318 and the filter variable portion 317because the rigidity of the second torsion springs 324 supporting theinternal variable portion 316 is great. Accordingly, the damage of theMEMS device 300, in particular, the damage of the first torsion springs322, due to the external shock, is prevented.

The fabrication process of the MEMS device 300 is similar to that of theMEMS device 100 according to the above first exemplary embodiment.However, for the ascending restriction stopper 340 and the descendingrestriction stopper 350 to be separated a predetermined distance fromthe peripheral portion of the external variable portion 318 and theframe peripheral portion 312, respectively, before the first substrate310 and the second substrate 330 are bonded together, a groove is formedby etching the upper surface of the first substrate 310 using apredetermined pattern not etching the lower surface of the secondsubstrate 330. By etching the upper surface of the first substrate 310,the thicknesses of the first torsion springs 322 and the filter springs323 are made thinner than the thickness of the second torsion springs324 so that the rigidity of the first torsion spring 322 and the filtersprings 323 can be made less than that of the second torsion springs324.

As described above, the MEMS device according to the exemplaryembodiments the present invention includes the stoppers restricting thedisplacement of the actuator in the height direction so that the damageof the MEMS device due to an external shock, and an increase of costsaccompanying the damage can be prevented.

While this invention has been particularly shown and described withreference to exemplary embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims.

1. A method of fabricating a microelectromechanical systems (MEMS)device, the method comprising: bonding a second substrate to a firstsubstrate; forming a frame and an actuator connected to the frame to becapable of performing a relative motion with respect to the frame bypartially removing the first substrate; and forming at least one stopperwhich restricts a displacement of the actuator in a direction along theheight of the actuator by partially removing the second substrate,wherein the forming of at least one stopper comprises forming anascending restriction stopper which restricts an upward displacement ofthe actuator and a descending restriction stopper which restricts adownward displacement of the actuator.
 2. The method of claim 1, whereinthe first and second substrates are formed of silicon.
 3. The method ofclaim 1, wherein the forming of an actuator comprises forming theactuator connected to the frame to be capable of pivoting with respectto the frame.
 4. The method of claim 1, further comprising partiallyetching a lower surface of the second substrate before bonding the firstsubstrate and the second substrate to allow an end portion of the atleast one stopper to be separated from the first substrate.
 5. Themethod of claim 1, further comprising partially etching an upper surfaceof the first substrate before bonding the first and second substrates toallow an end portion of the stopper to be separated from the firstsubstrate.
 6. The method of claim 1, wherein the forming of the actuatorcomprises: forming an external variable portion connected to the frameto be capable of pivoting about a first pivot axis with respect to theframe; and forming an internal variable portion located inside theexternal variable portion to be capable of pivoting about a second pivotaxis with respect to the external variable portion, the second pivotaxis being perpendicular to the first pivot axis.
 7. A method offabricating a microelectromechanical systems (MEMS) device, the methodcomprising: bonding a second substrate to a first substrate; forming aframe and an actuator connected to the frame to be capable of performinga relative motion with respect to the frame by partially removing thefirst substrate; forming at least one stopper which restricts adisplacement of the actuator in a direction along the height of theactuator by partially removing the second substrate; and forming a stagefixed to the actuator by partially removing the second substrate.
 8. Themethod of claim 7, further comprising partially etching a lower surfaceof the second substrate before bonding the first and second substratesto form a separation column provided between the actuator and the stage.9. A method of fabricating a microelectromechanical systems (MEMS)device, the method comprising: bonding a second substrate to a firstsubstrate; forming a frame and an actuator connected to the frame to becapable of performing a relative motion with respect to the frame bypartially removing the first substrate; forming at least one stopperwhich restricts a displacement of the actuator in a direction along theheight of the actuator by partially removing the second substrate; andforming a drive coil wound around a peripheral portion of the actuator;and arranging at least one magnet which forms a magnetic field thatcrosses current flowing in the drive coil.
 10. The method of claim 9,wherein the forming of the drive coil comprises: forming at least onedrive coil groove by etching a lower surface of the first substrate; anddepositing metal in the at least one drive coil groove.